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androidkotlinandroid-livedataandroid-viewmodel

Observe live data objects in fragment using activity context?

I'm using navigation bottom with shared ViewModel with all fragments inside navigation bottom but it throws this exception when recall fragment second time

java.lang.IllegalArgumentException: Cannot add the same observer with different lifecycles

I have tried to make all observers attached to activity not to it's fragment as below

1-Declare viewModel in fragemt

viewModel = activity?.run { 
          ViewModelProviders.of(this,viewModelFactory).get(SharedViewModel::class.java)
} ?: throw Exception("Invalid Activity")

2-Observer livedata object

viewModel.msg.observe(activity!!, Observer {
     Log.i(TAG,it)
})

3- remove observer

override fun onStop() {
    super.onStop()
    viewModel.msg.removeObservers(activity!!)
}

This code is working fine with me, but I wondering if my code is correct and working probably? thanks in advance

Solution

  • It is a common mistake we do while using live-data in fragment. Using this/activity on fragment can be duplicate. You should use viewLifecycleOwner for livedata observing in fragment.

    viewModel.msg.observe(viewLifecycleOwner, Observer {
            Log.i(TAG,it)
        })

    For more information, read this article https://medium.com/@cs.ibrahimyilmaz/viewlifecycleowner-vs-this-a8259800367b

    You don't need to remove the observer manually.